Everyone takes it for granted that repeated or strong enough strikes to the head will render a person unconscious. But what's the biological rationale behind it? Why would our bodies respond to a strong blow by shutting down? It seems to be contrary to the fight-or-flight respone, how is the body supposed to defend itself or escape if it shuts down? If anything, it would seem to make the most sense to experience strong bursts of adrenaline when getting hit. (Come to think of it, this probably happens...I can't recall from experience).